The First Automotive CFD Prediction Workshop was held in December 2019 at St
Anne’s College at the University of Oxford with the aim to assess the ability of
a broad range of computational fluid dynamics (CFD) methods to predict the flow
over realistic automotive geometries. Here, results from 53 simulation data sets
from 9 separate groups are analyzed for the open-source automotive DrivAer model
(in the fastback and estate variants). The represented CFD approaches include
Reynolds-averaged Navier-Stokes (RANS) approaches with a broad range of
turbulence models, as well as scale-resolving approaches such as wall-modelled
large-eddy simulation (WMLES) and hybrid RANS-LES methods (HRLM). A range of CFD
codes was used, including commercial, academic, and open source. Compared to the
two experimental data points, there was a large spread of CFD results. The
difference between drag predictions among HRLM and RANS methods is significant,
with an even larger mismatch for lift. The differences are found to be more
significant for the estate geometry than for the fastback, with the former
having larger areas of flow separation. In general it is found that the spread
of HRLM is smaller than those for RANS approaches, with HRLM grouping closer to
the range of experimental values. However, for HRLM, there is a systematic
underprediction of the front lift coefficient that is irrespective of the mesh,
turbulence model, and CFD code. Given that the majority of participants used the
same mesh and boundary conditions, and in some cases the same CFD code, it
suggests that also user choices around numerical schemes, convergence, and
turbulence model coefficients may have a sizable impact, which was not possible
to fully control in this first workshop. It is worth noting as well that the CFD
simulations were conducted in a free-air environment and did not model the
wind-tunnel geometry itself, which may also be an area requiring further study.
The DrivAer model exhibits numerous complex flow physics, i.e.,
laminar/turbulent separation, diffusion of momentum in turbulent shear layers,
and interactions of turbulent wakes with boundary layers. However, the nature of
a community-driven workshop and the lack of extensive experimental data means
that this article can only report the current state of the art and serve as a
reference for future workshops and a springboard for more focused future studies
where topics can be explored in greater detail.
